The present invention relates to an end-fitting for a flexible pipe for transporting, over long distances, a fluid which is under pressure and possibly at a high temperature, such as a gas, oil, water or other fluids. The invention relates most particularly to an end-fitting for a pipe intended for offshore oil operations.
The flexible pipes used offshore must be able to resist high internal pressures and/or external pressures and also withstand longitudinal bending or twisting without the risk of being ruptured.
They have various configurations depending on their precise use but in general they satisfy the constructional criteria defined in particular in the recommendations API 17 B and API 17 J drawn up by the American Petroleum Institute under the title “Recommended Practice for Flexible Pipe” and “Specification for Unbonded Flexible Pipe”.
A flexible pipe generally comprises, from the inside outwards:
an internal sealing sheath made of a plastic, generally a polymer, resistant to the chemical action of the fluid to be transported;
a pressure vault resistant mainly to the pressure developed by the fluid in the sealing sheath and consisting of the winding of one or more interlocked metal profile wires (which may or may not be self-interlockable) wound in a helix with a short pitch (that is to say with a winding angle close to 90°) around the internal sheath; the profile wires have a cross section in the form of a Z or a T, or derivatives (teta or zeta) thereof, or a U or an I;
at least one ply (and generally at least two crossed plies) of tensile armor wires wound with a long pitch, that is to say one whose lay angle measured with respect to the longitudinal axis of the pipe is less than 55°; and
an external protective sealing sheath made of a polymer.
Such a pipe, with a smooth internal bore, since it formed by the sealing sheath, is called a smooth bore.
In a pipe called a rough bore, a carcass consisting of an interlocked metal strip is also provided inside the internal sealing sheath, said carcass serving to prevent the pipe collapsing under external pressure. The pressure vault also contributes, however, to the crush strength.
Pipes may also include an intermediate or anti-collapse sheath placed between the pressure vault and the first armor ply or between two armor plies so as, should the external sheath be punctured, to prevent seawater from infiltrating as far as the internal sheath and impairing the mechanical performance of the flexible pipe.
The pipe end-fittings, also defined in the API 17J recommendations, must be produced under conditions ensuring both good fixing and good sealing. In general, these are achieved by crimping of the sheath, that is to say by partial radial penetration of a rigid element into the sheath.
Several types of end-fittings for flexible pipes using the internal sheath crimping principle are known. For example, document WO 99/19654 shows an annulus encircling the internal sheath, this annulus having either two O-ring seals or two ribs for sealing. In document U.S. Pat. No. 5,639,128, which relates to a rough bore pipe, a tubular sleeve is inserted between the carcass and the internal sheath so as to bear radially on the sheath during crimping, and the sheath is crimped by a deformable crimping ring which, when it is pushed axially, cooperates with a frustoconical stop, deforms radially inward and penetrates the sheath so as to lock it and seal it. Such a ring is also called a monocone. However, these documents do not relate to pipes provided with an intermediate sheath that also has to be crimped to seal it.
The Applicant has already developed an end-fitting for crimping the internal sheath and for crimping the intermediate sheath. The end-fitting includes a stepped part that can slide in a stepped cylindrical housing of the end-fitting, this part forming a bicone, that is to say having, at its two axial ends, an integral crimping ring (or lip); the bicone ensures, under axial compression causing the rings to deform, that the internal sheath is fixed and sealed at the front by cooperation with a tapered sleeve and that the intermediate sheath is fixed and sealed at the rear by cooperation with the pressure vault of the pipe, bolts providing said axial compression and allowing the stepped part to be brought up to the end-fitting and fixed thereto.
This construction is generally satisfactory, but it turns out in use that the manufacture is not simple, since many very precise contact adjustments have to be made on the stepped part, the mounting of which is not simple, especially if one considers that the pipe and end-fitting are of large diameter (for example forty centimeters or so) and heavy, that the constructional imperfections may make it difficult or impossible to adjust the stepped part and, above all, that it is very difficult to carry out a sealing test on the two sleeve crimpings. However, for safety reasons, such a prior test is being requested more and more frequently by users.
The objective of the invention is therefore to improve the existing end-fitting, by providing a construction which makes it possible, on the one hand, for it to be mounted for easily and, on the other hand, for sealing tests to be carried out.
The invention achieves its objective by means of a fixing end-fitting for a flexible tubular pipe, comprising as a minimum, from the inside outward, an internal sealing sheath made of a plastic, generally a polymer, a pressure vault formed by a short-pitch helical winding of a metal profile wire, an intermediate sealing sheath, at least one tensile armor ply wound with a long pitch and at least one external protective sealing sheath. The housing of the one end-fitting including a stepped part that can slide in a stepped cylindrical housing of the end-fitting and is designed to ensure, through two deformable crimping elements, that the internal sheath is fixed and sealed at the front (by cooperation with a bearing element, such as a tapered sleeve in the case of smooth-bore pipes or the carcass itself in the case of rough-bore pipes) and that the intermediate sheath is fixed and sealed at the rear. Bolts allow the stepped part to be brought up to the end-fitting and fixed thereto. The stepped part and the deformable elements are produced in the form of separate parts, namely the stepped part and two separate crimping rings. Not only is their assembly facilitated thereby, but above all it is possible to fit means for checking the sealing during assembly.
Advantageously, the rear deformable element is clamped to the intermediate sheath by a flange on the stepped part being clamped by means of bolts, these bolts being different from the bolts for clamping the stepped part to the end-fitting, and allowing the intermediate sheath to be crimped at the rear before the internal sheath is crimped at the front.
Advantageously, the rear deformable ring forms part of a bicone possessing, at the front, another deformable ring intended also to sink into the intermediate sheath. The bicone has a radial orifice for testing the sealing between the two deformable rings of the bicone. Preferably, an O-ring seal is also provided between the flange and the stepped part in order to prevent leaks during the sealing test. By virtue of these arrangements, it is easy to first crimp the intermediate sheath and check for leaks, before going on to crimp the internal sheath.
Advantageously, two O-ring seals are also provided between the stepped part and the end-fitting, and a radial orifice is provided for checking the sealing between these seals. One of these seals serving as a stop seal, for reducing any leaks that might appear between the stepped part and the vault of the end-fitting. The other seal serves merely for the sealing test procedure, so as to check the sealing of the stop seal.
The invention applies whenever an internal sheath and an intermediate sheath are to be crimped, and it relates to smooth-bore pipes and rough-bore pipes.